The logo in Header need to be decorative

[jorgeponto]

In header the element actually have this code:

<!--
<!--[if IE 8]>
          <img src="/assets/images/govuk-logotype-crown.png" class="govuk-header__logotype-crown-fallback-image" width="36" height="32">
          <![endif]-->
-->

As you have in svg logo w/ aria-hidden="true" and aria-focusable="false" to declare this element as decorative to assistive technologies you need something similar to the <img element. If not we got an image without alternative text.

So change to (add alt=""):

<!--
<img src="/assets/images/govuk-logotype-crown.png" class="govuk-header__logotype-crown-fallback-image" width="36" height="32" 
                 alt="">

-->